Micro-electro-mechanical systems elements such as those disclosed in JP-A-8-334709, JP-A-2000-28937, JP-A-10-48543 and JP-A-6-124341 have been proposed, and an array device in which such micro-electro-mechanical systems elements are arranged in a one- or two-dimensional array has been put to practical use.
FIG. 6 is a view showing a configuration of two elements of a rotational displacement spatial light modulator (SLM) element array device which is an example of a micro-electro-mechanical systems element array device. A driving circuit (see FIG. 7) is formed in a semiconductor substrate 1, and movable mirrors 2, 3 are formed in a surface portion of the semiconductor substrate 1.
Each of the movable mirrors 2, 3 is doubly supported in the air by a hinge 6 bridged between support columns 4, 5 which upstand on the surface of the semiconductor substrate 1, so as to be laterally inclinable about the hinge 6. Movable electrode films 7, 8 are formed integrally with the hinge 6 on both sides of a hinge shaft, respectively. On the surface of the semiconductor substrate 1, stationary electrode films 9, 10 are formed at positions opposing the movable electrode films 7, 8.
Next, a rotational displacement optical modulation element (hereinafter, referred to as SLM) which is based on electrostatic driving, and which is typified by an SLM element will be described. FIG. 7 is a diagram of the SLM. In FIG. 7, the movable mirror 2 and the movable electrode films 7, 8 are shown as an integrated one member. A driving circuit 11 which supplies an address voltage Va1 to the stationary electrode film 10, and an address voltage Va2 to the stationary electrode film 9 incorporates a memory circuit. When a displacement data Vd based on, for example, an image data is written from an external circuit into the memory circuit, the driving circuit 11 produces and outputs the address voltages Va1, Va2 on the basis of the displacement data Vd.
FIG. 8 is a diagram illustrating the inclining operation of the movable mirror of the SLM element shown in FIG. 7. When a bias voltage Vb is applied to the movable mirror 2 (movable electrode films 7, 8), the address voltage Va1 is applied to the stationary electrode film 10, and the address voltage Va2 is applied to the stationary electrode film 9, between the movable mirror 2 and the stationary electrode film 10, a first electrostatic attracting force corresponding to the voltage difference ΔV1=|Vb−Va1| between the components is produced, and, between the movable mirror 2 and the stationary electrode film 9, a second electrostatic attracting force corresponding to the voltage difference ΔV2=|Vb−Va2| between the components is produced.
In the case where the second electrostatic attracting force is sufficiently larger than the first electrostatic attracting force, the movable mirror 2 is inclined to the right as shown in FIG. 8A, and, in the case where the first electrostatic attracting force is sufficiently larger than the second electrostatic attracting force, the movable mirror 2 is inclined to the left as shown in FIG. 8B. At this time, the movable portion stops in a noncontact state at a position where the elastic torque due to a beam balances with the electrostatic torque in the inclination direction. When the electrostatic torque in the inclination direction becomes larger than the elastic torque due to the beam, the movable portion displaces until it contacts with the stationary portion on the substrate, and stops at the position.
A light source 12 emits light 13 to the movable mirror 2. The case where reflected light from the right-inclined movable mirror 2 is directed toward a projection optical lens 14 is set to the ON state. When the movable mirror 2 is not in the right-inclined state and is in the left-inclined state, the reflected light deviates from the projection optical lens 14 (the OFF state). When many SLM elements which are arranged in an array are irradiated with light in a given direction, and right- and left-inclined states of each SLM element are controlled, therefore, an optical image based on an image data can be projected through projection optical lens 14.